1. Field of the Invention
The present invention relates to a optical reflecting devices and more particularly to an apparatus for collecting or distributing radiant energy, into or from an optical waveguide.
2. Description of Background Art
Devices for collecting or concentrating a parallel beam of electromagnetic energy have conventionally employed reflective mirrors or refractive lenses. These devices collect energy in a broad spectrum from the entire area of the device and focus it onto a smaller area disposed at a considerable distance above or beneath the device and requires a fairly complex structure which occupies substantial volume.
Increasingly, light collection systems, including light detectors and concentrators, need to be configured for inputting light into a waveguide, such as an optical fiber or transparent rectangular plate, so it can be propagated along the waveguide by means of total internal reflection. In a conventional system, the spatially distributed light flux is input into a waveguide through one of its terminal ends using relatively large optical elements such as lenses and mirrors. Although the light guides themselves are typically slim and space efficient, the additional optics necessary for collecting or distributing the light over a large area leads to increased cost and system volume. In response to these shortcomings, the utility of the devices is hampered while numerous spatially-sensitive applications are rendered impractical.
Luminescent concentrators are also found in the industry for trapping incident radiation in a light guide by absorbing and re-radiating it in the form of scattered light at a longer wavelength using luminescent centers distributed in the volume of the light guide. However, because of the scattered nature of the reradiated light, only a portion of it can become trapped in the light guide by the total internal reflection, while the rest of the light escapes from the light guide. Furthermore, the luminescent centers can absorb or scatter already trapped light thus making the light guide less transparent and less efficient.
A holographic concentrator known in the art, utilizes a hologram layer that bends the incident light by means of diffraction so that it becomes trapped in a transparent light guide. However, at least a portion of the diffracted light is lost at each bounce from the same holographic layer guide due to re-coupling.
None of the previous efforts provides an efficient solution for light collection or concentration into a waveguide through its longitudinal face while maintaining a low system profile.
Conventional reflective mirror and refractive lens devices collimate electromagnetic energy across a broad energy spectrum from the entire area of the device and either focus it onto a smaller area disposed at a considerable distance above or beneath the device or collimate and direct it into a predetermined direction or onto a target. These devices are fairly bulky structures occupying substantial volume.
For example, in a conventional system, the primary optical element (e.g., mirror or lens) is focused at the location where the light emitting or light receiving element is disposed. Considering that the focus is usually located at a considerable distance from the primary optical element, the resulting volume formed by a three-dimensional shape enveloping the optical element's aperture and the focal point is considerably larger than the volume of the optical element itself. This increases system size, weight, and cost, while hampering utility of the system.
Many applications require the optical system to provide homogeneous irradiance distribution or another desired illumination pattern on a target. Examples are projection display systems requiring uniform light distribution from a light source on a target screen or optical collector where the light has to be collected and more evenly distributed across a light receiving device.
Numerous light processing systems require light to be input into a waveguide, propagated along the waveguide, and extracted from the waveguide to illuminate a designated target or pattern. In a conventional system, the light is extracted from a waveguide through one of its terminal ends and is further collimated by an optical system whose focus is disposed in the vicinity of the area where the light exits the waveguide. The inclusion of additional optics increases cost and system volume rendering the designs impractical in space-limited applications.
In another conventional system a planar waveguide is employed which extracts light from a lateral face of the waveguide by means of a number of light deflecting elements embedded into the waveguide or attached to its lateral face. Although this latter approach is more space efficient than the former one, the light comes out of the waveguide substantially uncollimated due to the inherent divergence of the light propagating in the waveguide which results in the substantial divergence of light extracted from the waveguide.
In addition, modern illumination systems often utilize compact and discrete light sources, such as Light Emitting Diodes (LEDs). Use of these light sources often results in unwanted glare problems, particularly in some general lighting applications or display lights. Typically, these problems are addressed by adding conventional and bulky optical systems, collimators and diffusers that at least partially negate the advantages of LEDs such as compactness and energy efficiency.
Accordingly, prior illumination efforts have failed to provide an efficient solution for extracting light from a waveguide through its longitudinal face with efficient light collimation. These needs and others are met within the present invention, which provides an improved optical system for distributing light along a waveguide and extracting the distributed light from the waveguide with minimum space consumption and improved light collimation.